Apparatus and method for forming materials

ABSTRACT

An apparatus and method for forming liquid spinning solution into a solid formed product whereby the solution is passed through at least one tubular passage ( 17 ) having walls formed at least partly of semipermeable and/or porous material. The semipermeable and/or porous material allows parameters, such as the concentration of hydrogen ions, water, salts and low molecular weight, of the liquid spinning solution to be altered as the spinning solution passes through the tubular passage(s).

TECHNICAL FIELD

This invention relates to an apparatus and method for forming spunmaterial, such as filaments, fibres, ribbons, sheets or other solidproducts, from a liquid spinning solution, such as a polymer solution(which term includes a protein solution or cellulose solution).

BACKGROUND ART

There is currently considerable interest in the development of processesand apparatus to enable the manufacture of polymer filaments, fibres,ribbons or sheets. It is theoretically possible to obtain materials withhigh tensile strength and toughness by engineering the orientation ofthe polymer molecules and the way in which they interact with oneanother. Strong, tough filaments, fibres or ribbons are useful in theirown right for the manufacture, for example, of sutures, threads, cords,ropes, wound or woven materials. They can also be incorporated into amatrix with or without other filler particles to produce tough andresilient composite materials. Sheets whether formed from fibres orribbons can be stuck together to form tough laminated composites.

Natural silks are fine, lustrous filaments produced by the silk-wormBombyx mori and other invertebrate species. They offer advantagescompared with the synthetic polymers currently used for the manufactureof materials. The tensile strength and toughness of the dragline silksof certain spiders can exceed that of Kevlar™, the toughest andstrongest man-made fibre. Spider dragline silks also possess highthermal stability. Many silks are also biodegradable and do not persistin the environment. They are recyclable and are produced by a highlyefficient low pressure and low temperature process using only water as asolvent. The natural spinning process is remarkable in that an aqueoussolution of protein is converted into a tough and highly insolublematerial.

According to an article by J. Magoshi, Y. Magoshi, M. A. Becker and S.Nakamura entitled “Biospinning (Silk Fiber Formation, Multiple SpinningMechanisms)” published in Polymeric Materials Encyclopedia, by theChemical Rubber Company, it is reported that natural silks are producedby sophisticated spinning techniques which cannot yet be duplicated byman-made spinning technologies.

Other known processes for producing filaments from liquid raw materialare disclosed in GB-A-441440 and U.S. Pat. No. 2,450,457. These knownprocesses pass the liquid raw material through rigid porous tubes.

Fibres produced by existing technological processes and apparatus sufferfrom the following disadvantages. Many show “die swell” which leads tosome loss of molecular orientation with a consequent degradation ofmechanical properties. This is not seen in natural silks which showstrongly uniaxial orientation. Furthermore, existing processes are notenergy efficient, requiring high temperatures and pressures to reducethe viscosity of the feedstock so that it can be forced through a die.Separate stages are often required, for example for further “draw-down”,to anneal the fibre with heat, and to process it through separate acidor alkaline treatment baths.

Disclosure of the Invention

It is an aim of the present invention to provide an improved method andapparatus for spinning a liquid spinning solution or “dope”.

According to a first aspect of the invention there is provided spinningapparatus for forming spun material from a liquid spinning solution, theapparatus including a die assembly having at least one tubular passagethrough which the liquid spinning solution is passed having at leastpartly permeable walls, wherein said walls defining the or each tubularpassage comprise at least one semipermeable membrane and/or at least oneporous membrane. Preferably enclosure means surround the walls. Theprovision of enclosure means allows components of fluent materialcontained in the enclosure means and in contact with the walls to passthrough the or each semipermeable or porous membrane. Alternativelycomponents of the liquid spinning solution passing through the or eachtubular passage may pass outwardly through the walls of thesemipermeable or porous membrane. In addition, since the or eachsemipermeable or porous membrane is generally flexible, it will benecessary to fill the enclosure means with a pressurised fluent materialto maintain the shape of the walls defining the tubular passage duringpassage of the spinning solution through the tubular passage.

According to a second aspect of the invention there is provided a methodof forming material by passing liquid spinning solution through at leastone tubular passage of a die assembly having at least partly prmeablewalls, wherein the walls of the or each tubular passage comprise atleast one semipermeable membrane and/or at least one porous membrane andin that the liquid spinning solution is treated, as it passes along theor each tubular passage, by components permeating through thesemipermeable or porous membrane of said walls. In this way fluentmaterial may pass inwardly into, or outwardly from, the or each tubularpassage through their semipermeable or porous walls.

The discovery of the way in which spiders produce dragline silk providesthe basis for the invention. We have found that by making the walls ofthe or each tubular passage at least partly permeable or porous,preferably selectively permeable along the length of the tubularpassage, which is preferably tapered, it is possible to controlproperties such as the pH, water content, ionic composition and shearregime of the spinning solution in different regions of the tubularpassage of the die. Ideally this enables the phase diagram of thespinning solution to be controlled allowing for pre-orientation of thefibre-forming molecules followed by a shear-induced phase separation andallowing the formation of insoluble fibres containing well-orientatedfibre-forming molecules.

Conveniently the walls defining the tubular passage(s) are surrounded bysaid enclosure means to provide one or more compartments. Thesecompartments act as jackets around the tubular passage(s). The or eachtubular passage suitably has an inlet at one end to receive the spinningsolution and an outlet at the other for the formed or extruded materialand is typically divided into three parts arranged consecutively, thefirst part allowing for the pre-treatment and pre-orientation of thefibre-forming polymer molecules in the liquid feedstock prior to formingthe material by draw down, the second region in which draw down of the“thread” takes place and which functions as a treatment and coatingbath, and the third part has an outlet or opening of restrictedcross-section which serves to prevent the loss of the contents of the“treatment bath” with the emerging fibre and to provide for thecommencement of an optional air drawing stage.

It will be appreciated that any solution or solvent or other phase orphases surrounding the fibre in the second part of the or each tubularpassage also serves to lubricate the fibre as it moves through and outof the tubular passage.

All or part of the length of each tubular passage typically has aconvergent geometry typically with the diameter decreasing in asubstantially hyperbolic fashion. According to G. Y. Chen, J. A. Cuculoand P. A. Tucker in an article entitled “Characteristic and DesignProcedure of Hyperbolic Dies” in the Journal of Polymer Sciences: PartB: Polymer Physics, Vol 30, 557-561 in 1992, it is reported that theorientation of molecules in a fibre can be improved by using a die witha convergent hyperbolic geometry instead of the more usual parallelcapillary or conical dies.

The geometry of substantially all or part of the or each tubular passagemay be varied to optimise the rate of elongational flow in the spinningsolution (dope) and to vary the cross-sectional shape of the formedmaterial produced from it. The preferred substantially hyperbolic taperfor part or all of the or each tubular passage maintains a slow andsubstantially constant elongational flow rate thus preventing unwanteddisorientation of the fibre-forming molecules resulting from variationin the elongational flow rate or from premature formation of insolublematerial before the dope has been appropriately preoriented. Aconvergent taper to the tubular passage of the die will induceelongational flow which will tend to induce a substantially axialalignment in the fibre-forming molecules, short fibres or fillerparticles contained in the dope by exploiting the well known principleof elongational flow. Alternatively, the principle of elongational flowthrough a divergent instead of convergent die can be used to induceorientation in the hoop direction that is approximately transverse tothe longitudinal axis of the extruded material.

The diameter of the or each tubular passage may be varied to producefibres of the desired diameter.

The rheology of the liquid feedstock in the tubular passage of the dieis largely independent of scale enabling the size of the apparatus to bescaled up or down. The convergence of the tubular passage allows a widerange of drawing rates to be used typically ranging from 0.01 to 1000 mmsec⁻¹. If fibres are being extruded they may typically have a diameterof from 0.1 to 100 μm. Typically the outlet of the tubular passage has adiameter of from 1 to 100 μm with the diameter of the inlet of thetubular passage being from 25 to 150 times greater depending on theextensional flow it is desired to produce. Tubular passages with acircular cross-section are used to produce fibres with circular crosssections. Tubular passages of alternative cross-sectional shapes can beused to produce fibres, flat ribbons or sheets of extruded materialswith other cross-sectional shapes.

All or part or parts of the walls of the or each tubular passage of thedie assembly are constructed from or formed or moulded from selectivelypermeable or porous membranes, such as cellulose acetate-based membranesheets. The membrane can be substituted with diethylaminoethyl orcarboxyl or carboxymethyl groups to help maintain protein-containingdopes in a state suitable for spinning. Other examples of permeable orporous membranes are hollow-fibre membranes, such as hollow fibresconstructed from polysulfone, polyethyleneoxide-polysulfone blends,silicone or polyacrylonitrile. The exclusion limit selected for thesemipermeable membrane will depend on the size of the small molecularweight constituents of the dope but is typically less than 12 kDa.

All or part of the walls of the or each tubular passage can heconstructed from selectively permeable or porous membranes in a numberof different ways. By way of example only a selectively permeable orporous sheet can be held in place over a groove with suitable geometrycut into a piece of material to form the tubular passage. Alternativelytwo selectively permeable or porous membranes can be held in place oneither side of a separator to construct the tubular passage.Alternatively a single sheet can be bent round to form a tubularpassage. A hollow tube of selectively permeable or porous membranematerial(s) can also be used to construct all or part of the tubularpassage. By way of example only, a variety of methods are available toshape the tube into a die as is commonly known to a craftsman skilled inthe art.

The use of selectively permeable or porous walls for substantially allor part or parts of the tubular passage(s) enables the proper controlwithin desired limits of, for example, the concentration offibre-forming material; solute composition; ionic composition; pH;dielectric properties; osmotic potential and other physico chemicalproperties of the dope within the tubular passage by applying thewell-known principles of dialysis, reverse dialysis, ultrafiltration andpreevaporation. Electro-osmosis can also be used to control thecomposition the dope within the tubular passage. It will be appreciatedthat a control mechanism receiving inputs relating to the product beingformed, for example the diameter of the extruded product and/or theresistance countered in the tubular passage, such as during extrusionthrough the outlet of the tubular passage, can be used to control, forexample, polymer concentration, solute composition, ionic composition,pH, dielectric properties, osmotic potential and/or otherphysicochemical properties of the dope within the tubular passage.

The selective permeability and/or porosity of the walls of the or eachtubular passage may also allow for the diffusion through the walls offurther substances into the tubular passage(s) provided that these havea molecular weight lower than the exclusion limit of the selectivelypermeable material from which the walls of the tubular passage(s) areconstructed. By way of example only the additional substances added tothe dope in this manner may include surfactants; dopants; coatingagents; cross-linking agents; hardeners; and plasticisers. Larger sizedaggregates can be passed through the walls of the tubular passage if itis porous rather than being simply semipermeable.

The compartments surrounding the walls of the tubular passage orpassages may act as one or more treatment zones or baths forconditioning the fibre as it passes through the tubular passage(s).Additional treatment can occur after the material has exited the outletof the tubular passage.

One or more regions of the or each tubular passage may be surrounded byone or more compartments arranged consecutively so as to act as a jacketor jackets to hold solution, solvent, gas or vapour in contact with theouter surface of the selectively permeable walls of the tubularpassage(s). Typically solution, solvent, gas or vapour is circulatedthrough the compartment or compartments. The walls of the compartment orcompartments are sealed to the outer surface of the walls of the tubularpassage(s) by methods that will be understood by a person skilled in theart. The compartment or compartments serve to control the chemical andphysical conditions within the or each tubular passage. Thus thecompartments surrounding the tubular passage(s) serve to define thecorrect processing conditions within the dope at any point along thetubular passage(s) In this way parameters such as the temperature;hydrostatic pressure; concentration of fibre-forming material; pH;solute; ionic composition; dielectric constant; osmolarity or otherphysical or chemical parameter can be controlled in different regions ofthe tubular passage as the dope moves down the length of the die. By wayof example only, continuously graded or stepped changes in theprocessing environment can be obtained.

Conveniently a selectively permeable/porous membrane can he used totreat one side of a forming extrusion in a different way to the otherside. This can be used, for example, to coat the extrusion or removesolvent from it asymmetrically in such a way that the extrusion can bemade to curl or twist.

All or part of the draw down process may typically occur within the dierather than at the outer face of the die assembly as occurs in existingspinning apparatus. The former arrangement offers advantage overexisting spinning apparatus. The distortion of molecular alignment dueto die swell is avoided. The region of the die assembly after theinternal commencement of the draw down taper can be used to applycoatings or treatments to the extrusion. Further, the last part of thedie assembly is water lubricated by the solvent-rich phase surroundingthe extrusion.

By way of example only the apparatus can be used for forming fibres fromdopes containing solutions of recombinant spider silk proteins oranalogues or recombinant silk worm silk proteins or analogues ormixtures of such proteins or protein analogues or regenerated silksolution from silkworm silk. When these dopes are used it is necessaryto store the dope at a pH value above or below the isoelectric point ofthe protein to prevent the premature formation of insoluble material. Itwill be appreciated that other constituents may be added to the dope tokeep the proteins or protein analogues in solution. These constituentsmay then be removed through the semipermeable and/or porous walls whenthe dope has reached the appropriate portion of the tubular passage inwhich it is desired to induce the transition from liquid dope to solidproduct, e.g. thread or fibre. The dope within the tubular passage canthen be brought by dialysis against an appropriate acid or base orbuffer solution to a pH value at or close to the pK value of one or moreof the constituent proteins of the dope. Such a pH change will promotethe formation of an insoluble material. A volatile base or acid orbuffer can also be diffused through the walls of the or each tubularpassage from a vapour phase in the surrounding compartment or jacket toadjust the pH of the dope to the desired value. Vapour phase treatmentto adjust the pH can also occur after the extruded material has left theoutlet of the die assembly.

The draw rate and length, wall thickness, geometry and materialcomposition of the or each tubular passage may be varied along itslength to provide different retention times and treatment conditions tooptimise the process.

One or more regions of the walls defining the or each tubular passagecan be made impermeable by coating their inner or outer surfaces with asuitable material to modify the internal environment in a length of thetubular passage using any coating method as will be understood by aperson skilled in the art.

The inner surface of the walls of the or each tubular passage can becoated with suitable materials to reduce the friction between the wallsof the tubular passage and the dope or fibre. Such a coating can also beused to induce appropriate interfacial molecular alignment at the wallsof the tubular passage in lyotropic liquid crystalline polymers whenthese are included in the dope.

A further embodiment allows for one or more additional components to befed to the start of the or each tubular passage via concentric openingsto allow two or more different dopes to be co-extruded through the sametubular passage allowing for the formation of one or more coats orlayers to the fibre or fibres.

A further embodiment utilises a dope prepared from a phase separatingmixture containing two or more components which, for example, may bedifferent proteins. The removal or addition of components through theselectively permeable and/or porous material can be used to control thephase separation process to produce droplets of one or more componentstypically with a diameter of 100 to 1000 nm within the bulk phase in thefinal extrusion. These can be used to enhance the toughness and othermechanical properties of the extrusion. The use of a convergent ordivergent die conveniently induces elongational flow in the droplets toproduce orientated and elongated filler particles or voids within thebulk phase. A convergent die will orientate and elongate such dropletsin a direction parallel to that of the formed product whereas adivergent die will tend to orientate the droplets in hoops transverse tothe direction of flow within the tubular passage. Both types ofarrangement can be used to enhance the properties of the formed product.Further it will be understood that the selectively permeable or porouswalls of the or each tubular passage can be used to diffuse in or outchemicals to initiate the polymerisation of filler particles.

The spinning apparatus with one or more tubular passages surrounded by acompartment or compartments to act as jackets can be constructed by oneor two stage moulding or other methods known to a person skilled in theart. It will be appreciated that a moulding process can be used tocreate simple or complete profiles for the or each tubular passage andthe outlet of the die assembly. Very small flexible lips can be formed,e.g. moulded, at the outlet to prevent the escape of the contents of thetreatment bath and act as a restriction to enable an optional additionalair drawing stage or wet drawing after the material has left the outletof the die assembly should this be required. The microscopic profile ofthe inner surface of the lips at the outlet can be used to modify thetexture of the surface coating of the extruded material.

By way of example only, the jackets and supports for the tubularpassages can be constructed from two or more components formed byinjection moulding or constructed in other ways as will be understood bya person skilled in the arts. It will be appreciated that this method ofconstruction is modular and that a number of such modules can beassembled in parallel to produce simultaneously a number of fibres orother shaped products. Sheet materials can be produced by a row or rowsof such modules. Such a modular arrangement allows for the use ofmanifolds to supply dope to the inlet of the tubular passage(s) and tosupply and remove processing solvents, solutions, gases or vapours toand from the jacket or jackets surrounding the tubular passages.Additional components may be added if desired. Potential modificationsto the arrangements shown will be apparent to persons skilled in theart.

Other methods of constructing spinning apparatus in which the walls ofthe tubular passages are substantially or partially constructed fromsemipermeable or porous membrane material will be known by a personskilled in the art. By way of example only these include micro-machiningtechniques. In addition it will be appreciated that walls of the tubularpassages substantially or partially constructed fromsemipermeable/porous material can be incorporated into other types ofspinning apparatus, such as electrospinning apparatus.

The or each tubular passage may be made self-starting and self-cleaning.It will be appreciated that blockage of spinning dies during thecommercial production of extruded materials is time-consuming andcostly. To overcome this difficulty, the walls of the tubular passagemay be constructed from an elastic material sealed into and surroundedby two or more jackets arranged in sequence. The pressure in each ofthese jackets can be varied independently by methods that will beunderstood by a craftsman skilled in the art. Pressure changes in thejackets can be used to change the diameter of different regions of thetubular passage in a manner analogous to a peristaltic pump to pump thedope to the outlet to commence the drawing of fibres or to clear ablockage. Thus a decrease in pressure in a jacket towards the outlet endof the tubular passage will dilate the elastic walls of the tubularpassage within the jacket. If the pressure is now raised in a secondjacket closer to the input end of the tubular passage a region of thewalls of the tubular passage running through this jacket will tend tocollapse forcing the dope towards the outlet. Alternatively, thepressure in the dope fed to the tubular passage could be increasedcausing the diameter of the elastic tubular passage walls to increase.It will be appreciated that both methods could be used together orconsecutively. With both methods the elasticity of the passage wallsenables the diameter of the tubular passage to be increased reducing theresistance to flow. With both methods it is to be noted that increasingthe pressure of the dope will also assist in start up and in clearingblockages in the tubular passage. It will also be appreciated by way ofexample only that the use of rollers such as are used in peristalticpumps can be used as an alternative means of applying pressure to pumpdope to the outlet to commence spinning or to clear a blockage.

The pressure in the sealed compartments surrounding the tubularpassage(s) may be controlled to define and modify the geometry of thetubular passage to optimise pinning conditions.

If the or each tubular passage has a convergent or divergent geometryalong all or part of its length, filler articles or short fibresincluded in the dope may be orientated as they flow through the tubularpassage by exploiting the well understood principle of elongationalflow. It will be understood that the substantially axial orientation ofsuch filler particles or short fibres will be produced by a convergenttubular passage while a divergent one will produce orientation in thehoop direction, that is approximately transverse to the long axis of theextruded material. Both patterns of orientation confer additional usefulproperties on the fibre. It will be appreciated that a convergent ordivergent geometry of all or part of the or each tubular passage willalso serve to elongate and orientate small fluid droplets of anadditional solvent or solution or other phase or phases or additionalunpolymerised polymer or polymers present in the dope as supplied to thetubular passage or arising by a process of phase separation within thedope. The presence of elongated and well orientated narrow inclusionsformed by either a convergent or divergent tubular passage can be usedto confer additional useful properties to the extruded material.

It will be appreciated that the direct drawing down of a fibre or otherformed product from liquid spinning solution within a region of atubular passage greatly improves the molecular orientation in the finalmaterial avoiding the disorientation produced by die swell produced byother methods of forming the final material. It also greatly reduces thepressure required to form material compared with the extrusion of fibrefrom a conventional restriction die.

The present invention seeks to alleviate some or all of the problemsassociated with the prior art by providing reliable apparatus and methodfor manufacturing materials with a highly defined and typically uniaxialmolecular orientation from spinning solutions. The use ofpermeable/porous tubing, preferably selectively permeable/porous tubing,for the construction of the walls of the tubular passage enables aprecise control of all parameters of the processing environment. Thisenables the processing environment to be precisely defined down thelength of the tubular passage. Precise control of the processingenvironment in the tubular passage enables the polymer concentration,molecular configuration and viscosity and other physical properties ofthe spinning solution to be kept at optimum values at all points alongthe tubular passage. The convergent geometry with cross-sectional areadecreasing non-linearly and preferably hyperbolically in substantiallyall or the first part of the tubular passage serves to align themolecules axially before the draw down process thus improving thequality of alignment in the final formed product.

The apparatus may be arranged in such a way that two or more fibres areformed in parallel and twisted around each other or crimped or woundonto a former or coated or left uncoated as desired. The fibres can bedrawn through a coating bath and subsequently through a convergent dieto give rise to a “sea and island” composite material as will beunderstood by a person skilled in the art. One or more rows of dies orone or more dies with slit or annular openings can be used to form sheetmaterials.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described, by way of exampleonly, with particular reference to the accompanying drawings, in which:

FIG. 1 is a generalised schematic representation of apparatus for theformation of extruded materials from a spinning solution;

FIG. 2 is a schematic cross-sectional view along the longitudinal axisof a die assembly of the apparatus shown in FIG. 1;

FIG. 3 is a schematic perspective view of the die assembly shown in FIG.2;

FIG. 4 is a schematic exploded view illustrating another embodiment of adie assembly of apparatus according to the invention; and

FIG. 5 is a view showing a number of die assemblies of FIG. 4 assembledtogether in a unit to enable a plurality of fibres to be extruded.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows apparatus for the formation of extruded materials from aspinning solution such as lyotropic liquid crystalline polymer or otherpolymers or polymer mixtures. The apparatus comprises a dope reservoir1; a pressure regulating valve or pump means 2 which maintains aconstant output pressure under normal operating conditions; a connectingpipe 3; and a spinning die assembly 4 comprising at least one spinningtube or die further described in FIGS. 2 to 5. A take-up drum 5 of anyknown construction draws out and reels up extruded material at aconstant tension exiting from the outlet of the die assembly 4. Thepressure regulating valve or pump means 2 may be any device normallyproducing a constant pressure commonly known to a person skilled in theart.

The arrangement shown in FIG. 1 is purely exemplary and additionalcomponents may be added if desired. Potential modifications to thearrangement shown in FIG. 1 will be apparent to persons skilled in theart. In use dope is passed from the feedstock reservoir 1 at a constantlow pressure by means of the regulating valve or pump means 2 via theconnecting pipe 3 to the inlet of the spinning die assembly 4.

The die assembly 4 is shown in greater detail in FIGS. 2 and 3 andcomprises a first spinning tube or die 8 upstream of a second spinningtube or die 12, the dies together defining a tubular passage 17 forspinning solution through the die assembly 4. The dies 8 and 12 are madeof semipermeable or porous materials, such as cellulose acetatemembranes or sheets. Other examples of suitable semipermeable or porousmaterials are diethylaminoethyl or carboxyl or carboxymethyl groupswhich help to maintain protein-containing dopes in a state suitable forspinning. Hollow-fibre membranes may also be used as thesemipermeable/porous membrane material, such hollow-fibre membranesbeing made from polysulfone, polyethyleneoxide-polysulfone blends,silicone or polyacrylonitrile. The exclusion limit selected for thesemipermeable membrane will depend on the size of the small molecularweight constituents of the spinning dope but is typically less than 12kDa.

The die 8 is held at its upstream end by a tapered adaptor 6 positionedat the inlet end of the die assembly 4 and at its downstream end by atapered adaptor 7 positioned internally in the die assembly 4. The die 8is held at its upstream end by the adaptor 7 and at its downstream endby a spigot 13 at the outlet of the die assembly 4. The die 8 has aconvergent, preferably hyperbolic, internal passage and the geometricaltaper is preferably continued with the internal passage of the die 12.This can be achieved during construction by softening a semipermeabletube or die on a warmed suitably tapered mandrel, or by other methods aswill be appreciated by a craftsman skilled in the art before fitting thespinning tube or die into the apparatus. The internal passages of thedies 8 and 12 together provide the tubular passage 17 for spinningsolution from the inlet to the outlet of the die assembly 4.

A jacket 9 surrounds the die 8 and is intended to contain a fluid, e.g.a solvent, solution, gas or vapour to control the processing conditionswithin the spinning tube or die 8. The jacket 9 is fitted with an inlet10 and an outlet 11 to control flow of fluid into and out of the jacket.A further jacket 14 surrounds the tube or die 12 and is fitted with afluid inlet 15 and a fluid outlet 16 to enable fluid, e.g. solvent,solution or gas, to be passed into and out of the jacket 14 in contactwith the semipermeable/porous walls of the die 12.

As an alternative to the die 8 shown having semipermeable walls a diemay be constructed from material which is not semipermeable but which ispreferably tapered, e.g. convergently, and may be temperature-controlledby circulating fluid at a predetermined temperature through the jacket9.

In operation spinning solution or dope, e.g. a polymer solution, is fedto the inlet of the die 8. As the dope passes along the tubular passage17 it is treated firstly as it passes through the die 8 and secondly asit passes through the die 12. The fluid passing through the jacket 9 maymerely serve to heat or maintain the dope at the correct temperature orprovide the correct external pressure to the walls of the die 8. In thiscase it is not essential for the walls of the die to be made ofsemipermeable or porous material. The temperature of the dies 8 and 12for the extrusion of protein-containing dopes should typically bemaintained at a temperature of about 20° C. but spinning may be carriedout at temperatures as low as 2° C. and as high as 40° C. The pressureof the fluid, liquid or gas, in the jackets surrounding the walls of thetubular passage 17 is typically maintained at a pressure close to thatat which the dope is supplied to the die assembly 4. However thepressure can be somewhat higher or lower depending on the geometry ofthe dies and the strength of the generally flexible semipermeable/porousmembrane. “Chemical” treatment of the dope occurs during “draw down”asthe dope passes through the die 12 although chemical treatment may alsooccur as the dope passes through the die 8 if the walls of the latterare at least partly made of semipermeable material. In FIGS. 2 and 3,the abrupt pulling away of the dope from the walls of the die 12 at 12Aindicates the internal draw down of the “fibre”. This is a uniquefeature of the invention as draw down in existing processes always startat the outer opening of a die (i.e. the extrusion orifice) and notbefore. The pulling away of the “fibre” from the die walls at 12A occursat a place in the tubular die 12 where the force required to produceextensional flow to create a new surface just falls below the forcerequired to flow the dope through the die 12 in contact with the diewalls. The position of 12A will depend on: the changing rheologicalproperties of the dope; the rate and force of drawing; the surfaceproperties of the die 12; the surface properties of the lining of thedie 12; and the properties of the dope and the aqueous phase surroundingthe dope.

It will be appreciated that the temperature, pH, osmotic potential,colloid osmotic potential, solute composition, ionic composition,hydrostatic pressure or other physical or chemical factors of thesolution, solvent, gas or vapour supplied to the jacket(s) control orregulate the conditions inside the tubular passage 17 as is commonlyunderstood by a craftsman skilled in the art. Chemicals in the fluidsupplied to the jacket(s) are able to pass through the semipermeable orporous walls of the tubular passage to “treat” the dope passingtherethrough. It is also possible for chemicals in the dope to passoutwardly through the semipermeable or porous walls of the tubularpassage 17. The fluids supplied to the dope will obviously depend on thetype of dope used and the semipermeable or porous membranes used.However, by way of example only, for the spinning of concentratedprotein solutions, the jacket 9 may contain 100 mM Tris or PIPES buffersolution, typically at a pH of 7.4, and 400 mM sodium chloride to helpmaintain the folded state of the protein. The jacket 14 may contain 100mM Tris or PIPES buffer solution at a lower pH, typically 6.3, and 250mM potassium chloride to encourage the unfolding/refolding of theprotein. High molecular weight polyethylene glycol can be added to thesolution in both jackets to maintain or reduce the concentration ofwater in the dope.

It will be realised that the spinning tube or die 12 can be hanked orcoiled or arranged in other ways between the tapered collar 7 and thespigot 13. The diameter and cross-sectional shape or the exit 13 can bevaried or adjusted to suit the diameter and cross sectional shape of theformed material. For a formed product having a circular cross-section,the typical diameter of the outlet is from 1 to 100 μm and the typicaldiameter of the inlet to the tubular passage would be from 25 to 150times greater than the outlet diameter depending on the extent of theextensional flow. It will be appreciated that the arrangements andproportions shown in FIG. 2 are purely exemplary and thus thatadditional components may be added if desired. Potential modificationsto the arrangements shown in FIG. 2 will be apparent to persons skilledin the art.

FIG. 4 shows a module containing three spinning tubes or dies 12 mountedwithin a housing defining three “jackets” 14, the same numbering beingused as in the previous embodiments to identify the same or similarparts. The arrangements and proportions shown in FIG. 2 are purelyexemplary and thus additional components may be added if desired.Potential modifications to the arrangements shown in FIG. 4 will beapparent to persons skilled in the art, including the provision of feweror more dies 12 or jackets 14.

FIG. 5 shows how two or more modular units constructed from theapparatus shown in FIG. 4 can be held together to enable a plurality ofextruded fibres to be produced. It will be appreciated that thearrangements and proportions shown in FIG. 5 are purely exemplary andthus additional components may be added if desired. Potentialmodifications to the arrangements shown in FIG. 5 will be apparent topersons skilled in the art.

The permeability or porosity of the walls of the tubular passage may bethe same throughout the length of the latter. Alternatively, however, ifthe tubular passage passes through more than one treatment zone thepermeability/porosity of the walls of the tubular passage may changefrom treatment zone to treatment zone by using different semipermeableor porous materials for the walls of the tubular passage. Thus the wallsof the tubular passage may comprise: semipermeable material of the samepermeability throughout the length of the passage; semipermeablematerial of different permeability for different portions of thepassage; porous material of the same porosity throughout the length ofthe passage; porous material of different porosity for differentportions of the passage; or semipermeable material for one or moreportions of the length of the tubular passage and porous material forone or more other portions of the tubular passage. As mentioned above,some portions of the walls of the tubular passage may be non-permeable.By way of example only, suitable semipermeable materials are: cellulosederivatives, Goretex (Registered Trade Mark), polysulfone,polyethylenoxide-polysulfone blends, and silicone polyacrylonitrileblends. By way of example only, the suitable porous materials are:polyacrylate, poly (lactide-co-glycolide), porous PTFE, porous silicon,porous polyethylene, cellulose derivatives and chitosan.

It will be appreciated that the apparatus is suitable for the formationof fibres or sheets from all solutions of lyotropic liquid crystalpolymers whether synthetic or man made or natural or modified orcopolymer mixtures or solutions of recombinant proteins or analoguesderived from them or mixtures of these. By way of example only theseinclude collagens; certain cellulose derivatives; spidroins; fibroins;recombinant protein analogues based on spidroins or fibroins, and poly(p-phenylene terephthalates). The method is also suitable for use withother polymers or polymer mixtures provided that they are dissolved insolvents, whether aqueous or non-aqueous, protein solutions or cellulosesolutions. It will also be appreciated that the use of one or moresemipermeable and/or porous treatment zones can be used for dies or dieassemblies having essentially annular or elongated slit openings usedfor the formation of sheet materials.

INDUSTRIAL APPLICABILITY

The invention has industrial application in the spinning of products.

1. Spinning apparatus for forming spun material from a liquid spinningsolution, the apparatus including a die assembly having at least onetubular passage through which the liquid spinning solution is passedwith at least partly permeable walls, wherein the said walls definingthe at least one tubular passage comprise at least one semipermeablemembrane and/or at least one porous membrane; and wherein an enclosuresurrounds said walls, wherein said enclosure comprises at least twocompartments isolated from each other, a first one of said at least twocompartments surrounding a first portion of said walls defining an inletportion of the at least one tubular passage and a second one of said atleast two compartments surrounding a second portion of said wallsdefining an outlet portion of the at least one tubular passage. 2.Spinning apparatus according to claim 1, wherein the die assembly has atleast two tubular passages through which the spinning solution ispassed, each ones of the at least two tubular passages being defined bywalls comprising at least one semipermeable membrane and/or at least oneporous membrane, and in that the at least two tubular passages passthrough each of said at least two compartments.
 3. Spinning apparatusaccording to claim 2, wherein a plurality of said die assemblies areassembled together in a unit.
 4. Spinning apparatus according to claim1, wherein each one of said at least two compartments has supply andremoval means for supplying fluent material to, and removing fluentmaterial from, the each one of said at least two compartments inquestion.
 5. Spinning apparatus according to of claim 1, wherein thecross-sectional area of said inlet portion of the at least one tubularpassage increases towards said outlet portion.
 6. Spinning apparatusaccording to claim 1, wherein the cross-sectional area of said inletportion of the at least one tubular passage decreases towards saidoutlet portion.
 7. Spinning apparatus according to claim 6, wherein thediameter of said inlet portion decreases substantially hyperbolicallytowards said outlet portion.
 8. Spinning apparatus according to claim 1,wherein said walls of the at least one tubular passage are made ofelastic, semipermeable or porous membrane material.
 9. Spinningapparatus according to claim 1, wherein said walls of the at least onetubular passage are partly coated on their inner and/or outer surfaceswith impermeable material to render said walls at least partlyimpermeable.
 10. Spinning apparatus according to claim 1, wherein innersurfaces of said walls of the at least one tubular passage are coatedwith friction reducing material.
 11. Spinning apparatus according toclaim 1, wherein concentrically arranged feed means are positioned atthe inlet end of the at least one tubular passage to supply said liquidspinning solution and one or more additional components to the at leastone tubular passage.
 12. Spinning apparatus according to claim 1 whereinsaid semipermeable membrane and/or porous membrane comprises celluloseacetate-based material, or substituted diethylaminoethyl, carboxl, orcarboxymethyl groups.
 13. Spinning apparatus according to claim 1,wherein said semipermeable membrane and/or porous membrane comprises ahollow-fibre membrane of polysulfone, polyethyleneoxide-polysulfoneblends, silicone or polyacrylonitrile.
 14. Spinning apparatus accordingto claim 1, comprising supply means for supplying celluloseacetate-based material, or substituted diethylaminoethyl, carboxyl, orcarboxymethyl groups.
 15. A method of forming spun material by passingliquid spinning solution through at least one tubular passage of a dieassembly having at least partly permeable walls wherein the said wallsof the at least one tubular passage comprise at least one semipermeablemembrane and/or at least one porous membrane, wherein a first fluidmaterial is supplied to a first compartment surrounding the at least onetubular passage for treating the liquid spinning solution, as it passesalong the at least one tubular passage, and in that a second fluidmaterial is supplied to a second compartment surrounding the at leastone tubular passage for treating the liquid spinning solution as itpasses along the at least one tubular passage by components permeatingthrough the semipermeable or porous membrane(s) of said walls.
 16. Amethod according to claim 15, wherein said first fluid material suppliedto the first compartment is liquid or gaseous.
 17. A method according toclaim 15, wherein components of said first fluid material supplied tothe first compartment pass through the semipermeable or porous walls ofthe tubular passage(s) to alter the pH, ionic composition, water contentand/or small molecular weight composition of the liquid spinningsolution passing through the at least one tubular passage.
 18. A methodaccording to claim 15, wherein the liquid spinning solution is treatedby diffusion, dialysis, reverse dialysis, ultrafiltration,electro-osmosis, pre-evaporation or a combination of these as it passesthrough the at least one tubular passage.
 19. A method according toclaim 15, wherein the liquid spinning solution comprises a phaseseparating mixture and in that the liquid spinning solution is treatedby diffusion of chemicals across the walls of the at least one tubularpassage to regulate the phase separation and semipermeablepolymerization process to produce filler particles or voids in theformed material.
 20. A method according to claim 15, wherein the length,area and/or position or thickness of the walls of the at least onetubular passage are varied to influence the rate or extent or positionat which the pH, ionic composition, or water content or small molecularweight composition are changed within the at least on passage.
 21. Amethod according to claim 15, wherein draw down of the spinning solutionto form the spun material commences within the at least one tubularpassage.
 22. A method according to claim 21, wherein the spun materialsubsequent to the draw down is treated or coated within the at least onetubular passage by components permearing through the semipermeable orporous membranes(s) of said walls.
 23. A method according to claim 15wherein said second fluid material supplied to the second compartment isliquid or gaseous.
 24. A new method according to claim 15, whereincomponents of said second fluid material supplied to the secondcompartment pass through the semipermeable or porous walls of the atleast one tubular passage to alter the pH, ionic composition, watercontent and/or small molecular spinning solution passing through the atleast one tubular passage.